The present invention relates to the radiology arts. It finds particular utility in medical applications, specifically diagnostic imaging, and will be described with particular reference thereto. However, it is to be appreciated that the invention may have other applications including quality control monitoring, subject treatment, subject monitoring, and the like.
Heretofore, nuclear cameras have been mounted to image patients from a plurality of directions. With appropriate software, diagnostic data from radiation emanating from the patient was reconstructed into tomographic images. In order to obtain the appropriate data for tomographic reconstruction, the nuclear camera detector or head was rotated in a circular orbit around the patient.
Because patients normally do not have a circular aspect ratio, the camera head moved further than necessary from the patient during the circular orbit. To reduce the image degradation attributable to this excessive patient-to-camera distance, elliptical orbits were instituted. However, clearance between the corners of the patient table and the nuclear camera head necessitated a larger than otherwise necessary ellipse. In order to reduce the patient to nuclear camera distance still further, a peanut shaped orbit was developed. In the peanut shaped orbit, the nuclear camera detector came close to the patient at the top and bottom surfaces but moved further away to clear the table corners. The peanut shaped orbit was most easily programmed into a nuclear camera whose detector was mounted for generally circular rotation about the patient. For a nuclear camera gantry designed for rectilinear movement, e.g. horizontal translating movement and vertical translating movement, an orbit r=b+a.vertline.sin.sctn.+z was developed. This orbit had larger lower lobes than upper lobes.
To facilitate automatic operation, the size of the above discussed orbit was selected by positioning the camera head at appropriate points along a selected orbit. Normally, the camera head was positioned with the appropriate clearance above, below, and to either side of the patient. The size of the orbit was adjusted to find the smallest orbit that would encompass all four of these camera head positions. In the orbit discussed above, the size of the orbit was changed by adjusting the size of the "a" and "b" terms. The z correction factor, which provided clearance for the table, remained fixed for all orbit sizes.
One of the problems with holding the z, or table clearance correction factor, constant is that the patient-to-detector head clearance was not optimized. The larger z correction factor necessary for larger orbits was excessively large at smaller orbits. Conversely, a smaller z correction factor, which would provide closer conformity of the camera head to the patient at small orbits, would result in a collision between the patient table and the camera head at larger orbits.
In accordance with the present invention, a new and improved method and apparatus are provided which changes both the size and the shape of the orbit.